Something I noticed on some artists

While exploring Derpibooru, I noticed something that repeats a lot on some artist and it’s the fact that many of their drawings have different poses but the same expression in all of them
 
just discovered that little detail and I find it someway funny
 
 
What are your thoughts about this?

once you get into a rut, it’s hard to get out. I think drawing sketches of different expressions might help. but I’m too lazy lol

It’s not even just expressions, I think different angles and concepts can get reused a fair bit too.